Hi, we have a homework policy here that this would fall under, but it's almost christmas so I will give you a little hint. "Drag Clutch!" No, that is not a purse a ...... might take to a Prom dance.
Picture this -- a light spring over the shaft, a flat metal washer, a flat leather washer (Hardware store Plumbing) the back of the propeller. The strength (compression or wire diameter) of the spring will determine the load to prevent free-spinning.